Plant Floor Playbook · PCBA Quality
30 Common PCBA Defects to Watch For
A practical inspection guide for surface-mount and through-hole production. Use it to recognize defect types, think about where to inspect, and decide which process data to review next.
A question from the production floor
“What are the main defects I should look for on our PCBA line, and where should we inspect them?”
A representative manufacturing question for J&K Custom Electronics.
The numbers identify checklist items; they are not a universal frequency ranking. Defect frequency varies with product design, materials, equipment, setup, and process controls. Use your own first-pass-yield, inspection, rework, and scrap data to build a line-specific Pareto.
Jump to a process group
Why start with solder paste? A 2004 research paper cites an estimate that 50–70% of defects in SMT assembly lines may be related to paste printing. Treat that as a historical industry estimate—not a guaranteed rate for every line or a figure for combined SMT and through-hole production. Your own production data is the right basis for prioritizing action. Read the study.
Process group
SMT solder paste & reflow
- 01
Solder bridging
Solder creates an unintended electrical connection between adjacent pads, leads, or conductors.
- 02
Insufficient solder / starved joints
Too little solder or incomplete wetting can leave a joint that does not meet the applicable workmanship or reliability requirements.
- 03
Tombstoning
A small two-terminal part stands on one end during reflow, often when forces at its two terminations are unbalanced.
- 04
Open joints and non-wetting
An open circuit may result when solder fails to wet a lead or pad, or when the joint is otherwise incomplete. Non-wetting is one possible cause of an open.
- 05
Poorly formed joints (“cold” solder)
An unsuitable thermal process or poor wetting can create an unreliable joint. A dull or grainy appearance by itself does not prove that a joint is defective.
- 06
Solder balls or beads
Small solder spheres may remain near a joint or on the solder mask. Assess their location and risk against the product’s acceptance criteria.
- 07
Excess solder
An excessive deposit or joint can obscure inspection, affect clearances, or contribute to bridging; evaluate the actual geometry and applicable criteria.
- 08
Head-in-pillow (HiP)
At a BGA connection, the solder ball and paste may fail to coalesce fully, creating a weak or intermittent connection that can be difficult to detect.
- 09
Solder-joint voiding
Gas pockets form within a joint. Their significance depends on package type, joint function, void location and size, and the agreed acceptance criteria.
- 10
Solder wicking
Solder travels away from the intended joint and up a lead or into a plated hole, potentially reducing solder available at the required connection.
Process group
Component placement & orientation
- 11
Misalignment / offset
A component sits off its intended pads, possibly reducing termination overlap or creating a clearance risk.
- 12
Missing component
A required part is absent because of a pick, feeder, placement, or handling error.
- 13
Polarity reversal
A polarity-sensitive part, such as a diode, LED, or polarized capacitor, is installed in the wrong direction.
- 14
Wrong component or value
The installed part does not match the bill of materials or approved assembly data, often due to setup, feeder, or material-control errors.
- 15
Billboarding / side-standing
A rectangular chip component stands on its narrow edge rather than resting on its terminations.
- 16
Incorrect face or orientation
A part is placed with an unintended face or orientation. Whether this affects function depends on the component and assembly requirements.
- 17
Skewed or rotated component
A component is rotated or skewed enough to reduce pad overlap, create clearance concerns, or violate the specified placement criteria.
- 18
Extra or foreign component
An unintended part or foreign object is present, perhaps after being dropped onto wet paste or introduced during handling.
Process group
Through-hole & wave/selective solder
- 19
Insufficient plated-through-hole fill
Solder fill does not meet the applicable workmanship requirements. Acceptance depends on product class, the governing standard revision, and customer requirements.
- 20
Pinholes or blowholes
Small cavities appear in a solder joint or plated barrel. Moisture, contamination, outgassing, and board-fabrication conditions may warrant investigation.
- 21
Lifted through-hole component
A component moves upward or loses its intended seating during soldering, handling, or fixture release.
- 22
Icicles or solder flags
Sharp projections or tails remain after soldering and may create clearance, safety, or reliability concerns.
- 23
Lead forming, clinching, or trim issues
Lead length, bend, clinch, or trimming is inconsistent with the assembly drawing or applicable acceptance requirements.
Process group
Board, component & handling damage
- 24
Lifted or delaminated pad
A copper land separates from the laminate, sometimes after excessive rework heat or mechanical force.
- 25
Cracked ceramic capacitor (MLCC)
Mechanical stress can crack a brittle ceramic body. Electrical symptoms may appear immediately or later in service.
- 26
Bent or non-coplanar leads
Leads do not sit in the intended plane or fail to contact the paste/pads as designed, which can prevent sound joints.
- 27
Flux residue or contamination
Residue or contamination may interfere with inspection, coating, electrical performance, or corrosion resistance. Some specified no-clean residues may be acceptable; assess the process and coating requirements.
- 28
Solder-mask damage or scratches
Damage exposes or affects the protective coating. Check for exposed copper, reduced spacing, contamination, and any electrical or environmental risk.
- 29
Board warpage (bow and twist)
The board bends or twists, affecting support, placement, connector fit, or solder-joint formation. See the PCB warpage guide for causes and troubleshooting.
- 30
Delamination or measling
Delamination is separation between laminate layers; measling is a different laminate condition involving localized whitening. They are not interchangeable terms, and acceptance depends on the applicable criteria.
Make inspection useful
Put the right detection gate at each process step
No single inspection technology finds every defect. Match each check to the defect, package, access, and control plan; validate that your equipment and inspection program can detect what you intend to catch.
After paste printing
Use solder-paste inspection (SPI), where available, to review deposit location and volume before parts are placed. Investigate trends in print offsets, insufficient deposits, or unintended paste.
Placement / post-reflow
Use pre-reflow checks and automated optical inspection (AOI) for visible placement, orientation, and solder conditions within the system’s validated coverage.
Hidden joints
Use X-ray inspection selectively for hidden connections such as BGA or bottom-termination packages and for void analysis when required. Detection limits vary; some defects can be difficult to distinguish.
Wave / final inspection
Inspect accessible through-hole joints after wave or selective soldering. At final inspection, assess board and component damage, contamination, and other product-specific requirements.
Acceptance matters: IPC-A-610 and customer specifications define workmanship requirements for the applicable product class and agreement. Use the current governing documents for pass/fail decisions. This checklist is an aid to troubleshooting, not a substitute for those criteria.
- Liukkonen and Tuominen, “Statistical Monitoring of Solder Paste Printing,” Journal of the Japan Institute of Electronics Packaging, 2004. J-STAGE article.
- IPC, “Using Lean Six Sigma to Optimize Critical Inputs on Solder Paste Printing.” IPC technical paper.
- IPC, technical paper discussing AOI and X-ray inspection of hidden package connections. IPC inspection paper.
Need help narrowing down a recurring PCBA defect?
Share the symptoms, process step, defect photos, and inspection or rework data. We can discuss practical next steps.
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